Method and apparatus for melting snow and ice

ABSTRACT

Disclosed in this invention is a method and device for de-icing, snow melting and thawing frozen ground. The invention is based on warm moisture-laden air that can be blown over the surface to be iced or thawed or it can be introduced into an enclosed area where de-icing, ground thawing or snow melting is desired. The device consists of three components: a hot water or a steam boiler with an associated pump; a plenum for heating and humidifying air; and a delivery unit or head that brings the moisture-laden air into contact with the surface to be de-iced or thawed. In one embodiment the boiler is replaced by a direct fired burner. The delivery unit may be an air blanket with multiple perforations attached to an air duct or an inverted saucer-like delivery head likewise attached to an air duct, coming from the plenum or it can be simply an enclosed space in which is located the object to be de-iced or thawed and into which the hot moisture-laden air is conducted.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/868,690, filed on Jun. 15, 2004, which in turn claims priority toCanadian Patent No. 2,432,599, filed on Jun. 17, 2003, under 35 U.S.C.119(d), the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to de-icing, ground thawing and snow meltingdevices and methods to carry out these practices. In particular, thepresent invention relates to such things as de-icing ice-coveredsurfaces such as aircraft, helicopter blades, walkways and driveways. Italso relates to ground thawing such as that necessary in theconstruction industry prior to pouring concrete slabs or doing winterwork on underground pipes and sewers. Finally, the device relates tosuch things as snow melting as in winter construction sites or generallyclearing snow wherever it is not possible to do so with plows andblowers such as roofs or thawing frozen water pipes or sewermaintenance.

2. Background of the Invention

In northern climates, de-icing of frozen surfaces, particularly aircraftand helicopter blades, is a frequent necessity. The most common methodof de-icing these vehicles is by spraying wings, fuselage and bladeswith a hot glycol water solution. The main function of the glycol sprayis to melt the ice and the snow already there and to warm the surface inorder to provide a brief period of protection against further icing.Many other hot liquid solutions, organic and inorganic, have beendescribed in patents and have been shown to work, but they all havemajor drawbacks. Glycol therefore remains the material of choice.De-icing a large aircraft can cost upwards of $10,000, and it isestimated that glycol sales to the airline industry exceed $200 millionper year. Infrared heating systems are also available for aircraftde-icing and have found some limited applications. Helicopter bladespresent a special problem as it is considered desirable to avoid gettingorganic or inorganic material, even glycol in the blade mechanisms.Various systems are described to de-ice helicopter blades using warmair. These usually involve the use of a sock or other form of cover overthe blades through which warm air is circulated. In Canada and othernorthern regions, there is a need to thaw the ground in construction,municipal works and other activities as concrete cannot properly be laidover frozen ground. Now that construction is a year round activity,builders are increasingly making use of ground thawing techniques. Twoapproaches to ground thawing are commonly used. In the first, the spaceover the area to be thawed is covered and warm air is introduced intothe space. In a second method, an array of flexible hose is laid overthe area to be thawed and covered with an insulating blanket. Hot wateror glycol is then circulated through the hose. Both methods are slow.Dry, warm air does not contain a lot of heat unless introduced at veryhigh temperatures; something that is not practiced in most applications.In the second method, higher temperatures can be used but only a smallfraction of the ground surface comes in contact with the hot hoses. Heattransfer is limited by the rate of transfer to the ground. Both methodsbeing relatively ineffective, the ground thawing process can hold uplarge construction projects for numbers of days or weeks at a very highcost. Thus, there appears to be a need for a less costly method ofde-icing of aircraft and helicopter blades and a faster, more effectivemethod for thawing ground around construction sites.

SUMMARY OF THE INVENTION

The present invention seeks to provide a method of de-icing, melting andthawing a surface including the step of directing warm moisture-ladenair to the surface.

This invention also seeks to provide an apparatus for de-icing, meltingand thawing surfaces, wherein the apparatus includes a plenum, anaqueous fluid supply, a heat source for heating the aqueous fluid, aforced air inlet configured for input of forced air into said plenumthrough the heated aqueous fluid to produce warm moisture-laden air, anda delivery device fluidly coupled to the outlet of the plenum that isconfigured to direct warm moisture-laden air to the surface.

The invention also seeks to provide an apparatus of de-icing, meltingand thawing surfaces, wherein the apparatus includes a plenum, a flameheated source, at least one nozzle, a forced air inlet configured forinput of forced air into the plenum through the frame heated source andspray of aqueous liquid, thereby producing warm moisture-laden air, anda delivery device fluidly coupled to the outlet of the plenum that isconfigured to direct warm moisture-laden air to the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a first embodiment of the invention.

FIG. 2 is another embodiment of the same invention showing an L-shapedplenum.

FIG. 3 is a schematic view of a second embodiment of the invention.

FIG. 4 is a bottom view of a first delivery device.

FIG. 4 a is an end view of said first deliver device.

FIG. 4 b is a bottom view of a second delivery device.

FIG. 4 c is a side view of the same device.

FIG. 5 is a schematic view of one device using a third embodiment of theinvention.

FIG. 5 a is a bottom view of a warm air delivery head.

FIG. 6 is a schematic view of a second device using the third embodimentof the invention, i.e. steam.

FIG. 7 is a fourth embodiment of the inventors showing a cutaway sideview.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic view of a first embodiment of the presentinvention 1. A liquid is heated in boiler 2. The liquid may includewater and glycol, specifically water and ethylene glycol or propyleneglycol, or simply water. Heated liquid leaves the boiler through outlethose 3 and returns to the boiler through return hose 4. The heatedliquid, preferably around 170 to 190° F. is circulated via a pump 5. Thepump 5 is generally electrical in nature and is well known in the art.The heated liquid, whether it is water or a water/glycol mixture, leavesthe pump 5 through outlet hose 6 and is directed to the top of acontainer, known as plenum 7.

In a first embodiment of this invention, plenum 7 is approximately fourto six feet square and approximately five to seven feet in height.Plenum 7 is preferably water proof and air tight and contains a catchreservoir 8 at its bottom portion. Hot liquid glycol and water or wateris collected in the reservoir 8 and returned through return hose 4 forreheating in boiler 2. The hot water supply hose 6 to the plenum 7 isconnected to a tubular member 9, having a plurality of nozzles 10.Nozzles 10 spray heated liquid into the incoming air, which is ambientair forced into the plenum by blower 15 powered by an electric motor 17.

The ambient air is forced to the bottom of the plenum 7 by afunnel-shaped structure 15 a. The hot liquid from nozzles 10 warms andsaturates the incoming ambient air which is forced upward past thenozzles through plenum cap 11 to the warm, moist air delivery nozzle 12.Thereafter, the warmed moist air is pushed through an insulated flexiblehose 13 to a delivery head 14. The delivery head 14 directs the air overthe surface to be thawed in such a manner as to provide direct intimatecontact between the moisture-laden air and the surface of the snow orice or frozen ground 16 to be thawed. The warm, moist air enters thedelivery head 14 through a fixture 19, which is basically a clampedentry area for flexible duct 13. The warm air, once inside the deliveryhead 14 exits, directly onto the surface to be thawed thereby losing agood portion of its heat, through opening 20. Also shown in FIG. 1, is apropane source 25 which enters boiler 2 via propane line 18. In thefirst embodiment the propane boiler is of known design and capable ofdelivering 900 BTUs. Finally, the direction of the incoming ambient airis shown generally as 28.

In FIG. 2, a slightly modified arrangement of the invention is shown.Plenum 7 is divided into downward and upward air flow chambers 26 and 27respectively. The air flow is marked as 28. The hot water or glycol fromthe boiler which supplies hose 6, has an auxiliary hose 6 a. Thus supplyhose 6 runs generally to supply piping 9 and nozzles 10 and auxiliaryhot water hose 6 a runs to hot water glycol supply hose 9 a and nozzles10 a and 10 b. The embodiment in FIG. 2 also includes a heat coil 29.The heat coil 29 helps to warm the air and in the embodiment shown, itis wetted by nozzles 10 b facing opposite to nozzles 10 a therebyincreasing the output of the system while eliminating the excessdroplets entrained in the air. The excess water or water glycol liquidis collected in a reservoir 8 and returned to the boiler through returnpipe 4.

In FIG. 3, a different embodiment of the invention is shown. Again,heated liquid, either in the form of water or water/glycol solution,leaves boiler 2, travels through circulation pump 5 and hot liquidsupply hose 6. Hot water supply hose 6, rather than going to nozzles asshown in previous figures, enters into a series of heating coils 29 andthen returns as usual through a return flow valve 4. The ambient airblown by blower 15 enters through air inlet 30, and follows the path ofarrows 35 and exits in a heated, moist condition through nozzle 36.Meanwhile, water which collects in catch basin 32 drips down toreservoir 31 is circulated upward by pump 33 through inlet hose 34.Inlet supply hose 34 is perforated with a number of holes 34A. Thus,ordinary water drips down around coils 29 wetting the coils such that asthe air 35 passes through the series of wetted coils, 29, it becomesmoisture laden and warmed and thereafter leaves at nozzle 36.

FIG. 4 is a bottom view of one embodiment of a delivery device which isof particular value for melting snow and ice on walkways and driveways.The device consists of a number of elongated flexible ducts or tubing 66from 12 to 18 inches in diameter. There are a number of apertures 67 onthe underside which permit the warm moist air to come in contact withthe surface to be melted. Tubes 66 are attached by junction hoses 68 tomanifold 69. Warm moist air is fed to the delivery device by duct 13.

FIG. 4 a is an end view of the device in FIG. 4.

FIG. 4 b shows the bottom 51 of a flexible mattress-type fabric deliverydevice 47, and FIG. 4 c shows a side view of the same device. Tiestrings 48 are secured at the top and bottom of the device by buttonclips 49. This creates a mattress-type effect which increases turbulenceof the warm water-laden air. This warm moist air which enters the devicethrough duct 13 escapes downwardly through orifices 50 towards thesurface to be melted. The top 52 of the delivery device is preferablyinsulated. The orifices are arranged to create about one half inch ofstatic pressure inside of the device such that it retains its form andcan be maneuvered as required over the surface to be melted. A lesserpressure created between the delivery device and that by escaping airwill in general maintain a separation between the surface and thedevice.

FIG. 5 shows the side view of another warm air delivery head 54 and 5 ashows a bottom view of the same device. Warm moisture-laden air entersthe delivery head through insulated duct 13. It first enters upperchamber 55 and then moves downwardly to chamber 56 through orifices 57.Orifices 57 are made in a size and quantity to produce a robust exit ofthe moisture-laden air on to the surface to be de-iced or thawed whichwill create about one-half inch of static pressure in the space abovethe orifices.

FIG. 6 illustrates the steam embodiment of the invention. Steam boiler37 produces steam which flows through outgoing line 38. Outgoing line 38then separates into a first branch line 39 which runs into closed coils43 and a second branch line 40 which leads steam to steam jet nozzles41. Modulating valves 53 regulate the steam pressure to steam nozzles 41and coils 43. As incoming air flows in the direction of arrows 35, itencounters nozzles 41 and steam coils 43. It exits at 36 as heatedmoisture-laden air. Condensed steam 42 is collected by catch basin 44and returned via pipe 45 by pump 5 to boiler 37. Steam from coils 43exits to boiler 37 by pipe 46.

FIG. 7 is a schematic view of another embodiment of the invention.Blower 15 forces ambient air through a heat resistant plenum 65. Theambient air moves in the direction of arrows 35. The air firstencounters burner jets 63 which are fed by a propane source 61 throughpropane line 62. In operation the flames of these jets heat the air upto about 800° F. Obviously this hot dry air is unacceptable for aircraftde-icing operations. A water supply 58 feeds water through pump 59 towater pipe 60 to water nozzle 64. When the hot dry air encounters waternozzle 64 spray, it is cooled to about 150° F. to 180° F. and becomesclose to being saturated. This warm moisture-laden air then leavesnozzle 36 and is directed to a delivery head (not shown in FIG. 7).

In one embodiment, the present invention seeks to provide a method ofde-icing, melting and thawing surfaces, snow and ice and frozen ground,comprising: heating an aqueous liquid in a boiler to a high temperaturebelow the boiling point; directing said heated liquid into a series ofnozzles in a closed plenum; blowing ambient air into said plenum andthrough heated spray liquid emitted from said nozzles; directing heatedand moisture-laden air into an outlet duct; and directing said heatedand moisture-laden air from said duct to a delivery device that bringssaid moisture-laden air in direct contact with said surfaces, snow andice and frozen ground, thereby melting and thawing same.

In another embodiment, this invention also seeks to provide an apparatusfor de-icing, melting and thawing surfaces, snow, ice and frozen groundcomprising: a boiler with an aqueous liquid adapted to be heated; anoutlet hose adapted to carry liquid from said boiler; an inlet hoseadapted to return liquid to said boiler; a series of pipes and nozzlesconnected to said outlet hose; a circulating pump adapted to move saidliquid from said boiler through said outlet hose and said pipes andnozzles; a plenum-type housing adapted to contain said nozzles; a bloweradapted to introduce ambient air into said plenum-type housing; said airin operation being forced through said heated liquid from said nozzles;an outlet connected to said plenum-type housing and an outlet ductconnected to said outlet; said outlet duct being adapted to directwarmed, moisture-laden air to a delivery head structure; said deliveryhead structure being proximate to either said surface, snow and ice, orsaid frozen ground, thus permitting said warm, moisture-laden air topass there through such that melting or thawing occurs.

In a third embodiment, the invention also seeks to provide a method ofde-icing, melting and thawing surfaces and frozen ground comprising:heating a liquid in a boiler until it becomes vaporized into steam;directing a first portion of said steam through a series of enclosedcoils in a plenum-type housing; directing a second portion of said steamthrough a series of nozzles located in said plenum-type housing;introducing and blowing ambient air through said plenum, past saidnozzles and said coil; directing moisture-laden ambient air out of saidplenum-type housing to a duct and delivery head, thereby melting ice,snow or frozen ground.

In yet another embodiment, the invention also seeks to provide a methodof de-icing, melting and thawing surfaces and frozen ground comprising:heating an aqueous liquid in a boiler until it becomes vaporized intosteam; injecting said steam into a plenum-type housing through a seriesof nozzles located in said plenum-type housing; simultaneously injectinga spray of finely divided water particles in very near proximity to theinjected steam; blowing ambient air into said plenum, and passed saidnozzles and injected spray of water particles and directing warmedmoisture-laden air out of said plenum-type housing to a duct anddelivery head, thereby melting ice, snow and frozen ground.

Control of the temperature of the moisture-laden air is done by the useof a valve controlled by a thermostat that measures the temperature ofthe outgoing air and adjusts the flow of steam accordingly. Control ofthe moisture content is done by measure of a wet bulb temperaturemeasuring device or humidistat that control the amount of liquid waterinjected by the spray nozzles.

In an exemplary embodiment, this invention also provides an apparatusfor melting snow, ice and frozen ground comprising: a boiler adapted toheat an aqueous liquid to a temperature below the boiling point; a firstcirculating pump; an outlet line; an inlet line; a series of enclosedcoils located in a plenum-type housing and adapted to carry said heatedliquid; a separate, unheated water supply and second circulating pumpadapted to carry said unheated water to nozzles and direct said water atsaid enclosed coils; a blower adapted to move ambient air past saidnozzles and said enclosed coils to an outlet of said plenum-type housingand through a delivery duct and delivery head located proximate to asurface to be melted; and a reservoir adapted to catch surplussaturating water and direct it back to said second circulating pump.

In another embodiment, this invention seeks to provide an apparatus formelting snow, ice and frozen ground comprising: an elongated plenum-typehousing; a blower attached to one end of said plenum-type housing; saidblower, in operation, adapted to force ambient air into said housing;said apparatus further comprising: an open flame heat source located insaid plenum-type housing proximate to said blower; a fine water sprayapplicator located in said plenum-type housing downstream from said openflame heat source; wherein, in operation, incoming ambient air is heatedto a high temperature by said heat source and thereafter, cooled andmoistened by said fine water spray applicator, thereby producing warmmoisture-laden air at a temperature less than 200° F., which exits saidplenum-type housing at an opposite end from said blower to a deliveryhead proximate the snow and ice to be melted.

The rate of thawing that can be achieved by a stream of air isproportional to the amount of heat that is carried by that airstream.This in turn depends in part upon the temperature of the air, but moreimportantly, it depends upon the moisture content of the air. Air with ahigh degree of humidity contains more heat than dry air. This is mostapparent in saturated air at higher temperatures. At one end of thespectrum is 100% water vapor, i.e. live steam, (which must be at 212° F.in order to exist at atmospheric pressure). Cooling one pound of livesteam by, say 40° F., to convert it into liquid water at 172° F.releases 1000 BTUs of heat.

In order to get 1,000 BTUs of heat from one pound of dry air, one wouldhave to cool it by 4000° F. More realistically, one would have to use100 times more air, i.e. we would cool 100 lbs of air by 40° F. Lowerconcentrations of water vapor in air carry lower amounts of energy, butthe amounts are still impressive. Air that is saturated at 175° F. maybe thought of as half steam and half air. It has half the energy of livesteam without being nearly as dangerous to handle. Near the other end ofthe spectrum, e.g. at 70° F., air that contains no moisture, has anenthalpy, (i.e. energy content), of 17 BTUs per pound. Air at the sametemperature, which is at 100% relative humidity has an enthalpy twice ashigh, i.e. 34 BTUs per pound. For saturated air, the energy contentincreases dramatically as temperature is increased. At 150° F., air thatcontains no moisture has an enthalpy of 36 BTUs per pound, whereas if itis humidified to 100% relative humidity, it will have an enthalpy of 275BTUs per pound. Thus, at this temperature, by adding moisture, theenergy content of the air can be increased more than seven fold. At 180°F. the increase is more like 15 fold. Another way to look at it is thatwater saturated air at 150° F. contains more heat energy than dry air at1000° F. Saturated air at 180° F. has more heat energy than dry air at1500° F. Even these comparisons may understate the capacity ofmoisture-laden air to melt ice or snow.

Since most applications that require rapid de-icing do not allow the useof temperatures in the 1000 degree range, de-icing using warm dry air isoften unacceptably slow. Such is the case for de-icing aircraft. At thepresent time, the most widely used method of de-icing aircraft is byspraying with hot water/glycol solution. Liquid temperatures in therange of 150 to 180° F. are typically used. The length of time requiredto do the job is of the order of 15 minutes. De-icing using normal warmair at a comparable temperature can take 10 times as long; a length oftime that is not acceptable for a loaded aircraft.

Moisture-laden air presents a more plausible option. At 150° F., astream of saturated air will melt ice seven times more quickly than airthat was heated to the same temperature without the addition ofmoisture. Saturated air at 180° F. has a heat content that is more than10 times greater than dry air at the same temperature, and its relativecapacity to melt ice is in that range. With a suitable air deliverysystem, the present invention can attain de-icing rates up to ten timesgreater than warm air alone. This puts it in the same class as glycol,time wise, but at a fraction of the cost and environmental impact. Aglycol-based aircraft de-icing system has added benefit over anair-based system in that it leaves a residual coating of glycol that canoffer some additional short-term residual protection. In one embodimentof the present invention, as conceived for aircraft de-icing, 40% to 60%propylene glycol is used within the system itself so that after the iceand snow has been melted away, this solution can be used as a finishingspray to provide the same continuing short-term protection.

The production of moisture-laden air and its delivery to the surface tobe thawed can be achieved in a number of ways. The most practicalvehicles for producing moisture-laden air are described herein. Theyare: (a) hot water spray, (b) hot water wet-coil, (c) cold water sprayedhigh temperature blown air, or (d) steam. Devices to effectively deliverthe moisture-laden air will be described as follows:

(a) Hot Water Spray System:

Any of a variety of commercially available water heaters may be used,provided they have adequate capacity. The heater may deliver the hotaqueous liquid directly to the plenum or it may deliver it indirectlythrough a heat exchanger. It may be fuel fire, (natural gas, propane,oil or even wood), or electrical. However, because of the large amountsof energy required, natural gas, propane or oil are the preferred energysources. An optional hot water coil may be used to provide supplementalheat to the leaving moisture-laden air. This will serve to convert intowater vapor, any residual water droplets that may be in the airstream.In some applications, it may be considered desirable to lower therelative humidity of the moisture-laden airstream, by raising thetemperature, in order to avoid condensation in the duct leading to thedelivery head. Hot water or water/glycol mix may be used, instead ofwater, as the source of moisture and the heat transfer medium. Whenwater/glycol mix is used as spray, the moisture content will be lowerthan when water alone is used. Consequently, the energy content of theairstream will be lower by few percent if water/glycol is used. Themoist air will also contain some glycol vapor. The ratio of water vaporto glycol vapor in the airstream will be determined by the relativevapor pressures of the two liquids at the given temperature. As a roughguide, glycol will constitute about 2% of the vapor if the liquid is 50%glycol. The pumping system should be capable of circulatingapproximately 8 GPM per 100,000 BTU of boiler heating capacity. Thecirculation pump must also have the capability of achieving this whileovercoming the resistance offered by the spray nozzles in thehumidification chamber.

(b) The Hot Water Wet-Coil Method:

A blower introduces air into a plenum using a duct in which are situateda series of coils. The actual number of coils (or rows within a coil),will be determined by the application as well as other elements of thedesign, but in general it will be significantly more than would be usedto simply heat the air without the addition of water vapor. Acirculating pump circulates water over the face and through the core ofeach of the coils, keeping their entire surface wet. A reservoircollects water that is in excess of what is required for evaporation.Thereafter, the water can be re-circulated. Water must be added fromtime to time to the reservoir to compensate for evaporation. The coilsare heated by hot water or hot water/glycol mix supplied by a hot waterheater of suitable capacity. The flow rate from the boiler, itscapacity, et cetera, must be engineered to take into account the largequantities of heat needed to evaporate the water in addition to thatrequired to heat the air.

(c) Cold Water Sprayed High Temperature Blown Air Method:

An elongated circular horizontally deposed plenum is used at one end ofthe plenum is an operative communicating through an operator to ablower. The blower forces ambient outside air into the plenum. Proximatethe air intake is a flamed heat source which uses as a fuel propane,natural gas or fuel oil. As the ambient air is forced into the plenum bythe blower, it is heated upwards to around 800° F. Thereafter the hightemperature heated air passes through a series of fine cold waterdroplets emitted by nozzles. This not only cools the air toapproximately 150° F. to 180° F. but also inserts moisture into the airclose to or at the saturation point. The warm moisture-laden air thenleaves the plenum and is directed through a duct to a delivery headwhich brings warm moisture-laden air in contact with snow, ice or frozenground.

(d) Steam Method:

The blower and plenum arrangement are essentially similar to that shownfor the wet coil method. In this arrangement, air entering the plenum,encounters live steam introduced from a steam boiler and then flowsthrough a steam heated coil. The purpose of the coil is to remove waterdroplets that form as the steam heats the incoming cold air. Themoisture-laden air, free of any water in liquid form, may then beconducted to the delivery head.

While the hot liquid required in method (a) and method (b) wouldnormally be produced as required, directly by a hot water heater, thereare circumstances where it is preferable to provide the hot water, ormore generally the hot liquid, from a reservoir. Such a circumstancewould be where use is intermittent and very large quantities of heat arerequired for a short period. Other circumstances may occur where theclose proximity to the flames inherent to a gas, propane or oil-firedhot water heater, poses a risk of fire or explosion. In this lattercircumstance, the reservoir may be mounted on a truck or trailer so thatit may be brought directly to the site where deicing is required. Suchmight be the case for deicing aircraft or helicopters. In theseconfigurations, i.e. using fixed or mobile reservoirs, the circulatingpump and hoses described under method (a) and method (b) would beassociated with the reservoir, and would circulate the liquid throughthe plenum arrangement and back to the reservoir; the supply and return,from and to the reservoir being constructed according to means, wellknown in the trade, that minimize mixing between the cooler returningliquid and the hot liquid in the reservoir.

In order to achieve the desired result of efficiently deicing a surface,it is important to get good heat transfer from the airstream to thesurface in question. Different applications are best served with a heatdelivery head designed to best suit that application.

For de-icing aircraft, an air delivery system consists of gantry housinga duct to carry the moisture-laden air that can be positioned and movedover the aircraft fuselage and wings. The moisture-laden air isconducted into a diffuser that in turn conducts the air over the surfaceto be de-iced, in near proximity to the surface or lightly touching thesurface. The diffusor is made of soft material to avoid contacting thesurface of the wing or fuselage with a hard surface. The objective is toensure that most of the heat energy in the airstream is transferred tothe surface. Because most of the heat energy in moisture-laden air isheld at the higher temperatures, it is relatively easier to achieveefficient transfer of heat from a moisture-laden airstream to the coldsurface than with air that is dry. When starting with 170° F. air thatis at or near saturation, cooling the airstream to 120° F. will capture80% of the heat energy initially imparted to that air. It is notnecessary to get a large degree of cooling of the air in order for it togive up most of its energy. This is illustrated by the followingexample: if one lb of air taken at 32° F. and simply heated to 132° F.,it will absorb 25 BTU and have an enthalpy of 35 BTU. If it is thencooled and allowed to escape at 72° F., it brings with it 22.5 BTU. Theamount of heat that was used for de-icing, at a maximum, is 12.5 BTU,i.e. (35-22.5) the efficiency can be no more than 50%. By comparison,one lb of air heated and saturated with water, to 132° F. will absorb155 BTU and have an enthalpy of 165 BTU/lb. If this air loses heat andescapes at 72° F., it will bring with it 35 BTU. The difference, 165-35,i.e. 130 BTU that has been used to do the work, i.e. an efficiency of84%. The differences between dry and moisture-laden air is even morepronounced at higher temperatures. For this reason, air leaks, always aproblematic in temporary enclosures, are far less important ifmoisture-laden air is the heating medium.

1. A method of de-icing, melting and thawing a surface, the methodcomprising directing warm moisture-laden air to the surface.
 2. Themethod according to claim 1, wherein prior to the step of directing, themethod further comprises the step of producing said warm moisture-ladenair.
 3. The method according to claim 1, wherein prior to the step ofdirecting, the method further comprises the step of providing heat andmoisture to air, thereby producing said warm moisture-laden air.
 4. Themethod as claimed in claim 2, wherein said warm moisture-laden air isproduced by conducting air through a warm spray of aqueous liquidthereby adding heat and moisture thereto.
 5. The method as claimed inclaim 4, wherein said warm moisture-laden air is produced by furtherconducting said air through one or more heated coils.
 6. The method asclaimed in claim 2, wherein said warm moisture-laden air is produced byconducting air through one or more wetted heated coils thereby addingheat and moisture to said air.
 7. The method as claimed in claim 2,wherein said warm moisture-laden air is produced by conducting airthrough a spray of steam and through one or more heated coils therebyadding heat and moisture to said air.
 8. The method as claimed in claim2, wherein said warm moisture-laden air is produced by conducting airthrough a flame heated source thereby heating said air, and by passingsaid heated air through a spray of aqueous liquid thereby cooling andadding moisture to said heated air.
 9. The method as claimed in claim 2,wherein said warm moisture-laden air is produced by heating an aqueousliquid, spraying said heated liquid within a plenum and forcing air intosaid plenum through said heated liquid spray.
 10. The method as claimedin claim 2, wherein said warm moisture-laden air is produced by heatingan aqueous liquid until it becomes vaporized, directing a first portionof said vapor through one or more heating coils within a plenum therebyheating said one or more coils, directing a second portion of said vaporthrough one or more spray nozzles within said plenum thereby providing asteam spray therein, and forcing air into said plenum through said vaporspray and said heating coils.
 11. The method as claimed in claim 4wherein said aqueous liquid comprises ethylene glycol.
 12. The method asclaimed in claim 4 wherein said aqueous liquid comprises propyleneglycol.
 13. An apparatus for de-icing, melting and thawing a surface,the apparatus comprising: a plenum; an aqueous fluid supply for input ofaqueous fluid within said plenum; a heat source for heating said aqueousfluid; a forced air inlet configured for input of forced air into saidplenum through said heated aqueous fluid to produce warm moisture-ladenair; and a delivery device fluidly coupled to an outlet of said plenumand configured to direct said warm moisture-laden air to the surface.14. The apparatus as claimed in claim 13, further comprising one or moreheated coils located within said plenum and disposed so to add heat tosaid warm moisture-laden air.
 15. The apparatus as claimed in claim 13,wherein said heated aqueous fluid is provided from said heat source tosaid plenum via said aqueous fluid supply.
 16. The apparatus as claimedin claim 15, wherein said fluid supply comprises one or more nozzlesconfigured to introduce a spray of said heated aqueous fluid into saidplenum, said forced air inlet configured for input of forced air throughsaid spray.
 17. The apparatus as claimed in claim 16, wherein said heatsource comprises a boiler fluidly coupled to said one or more nozzles.18. The apparatus as claimed in claim 17, wherein said heat sourcefurther comprises a heat exchanger.
 19. The apparatus as claimed inclaim 15, wherein said plenum comprises a reservoir adapted to receiveexcess aqueous fluid and return said excess liquid to said heat source.20. The apparatus as claimed in claim 13, wherein said aqueous fluidcomprises an aqueous liquid, and wherein said heat source comprises oneor more heated coils located within said plenum and operatively disposedso to be wetted by said fluid supply, said forced air inlet configuredfor input of forced air through said one or more wetted heated coils toproduce said warm moisture-laden air.
 21. The apparatus as claimed inclaim 13, wherein said aqueous fluid comprises steam.
 22. The method asclaimed in claim 13, wherein said aqueous fluid comprises ethyleneglycol.
 23. The method as claimed in claim 13, wherein said aqueousfluid comprises propylene glycol.
 24. The apparatus as claimed in claim13, wherein said delivery device comprises a delivery duct operativelycoupled to a delivery head, said delivery head comprising an inflatablemember with a lower surface comprising a plurality of apertures todeliver said warm moisture-laden air to the surface.
 25. The apparatusas claimed in claim 13, wherein said delivery device comprises adelivery duct operatively coupled to a delivery head, said delivery headcomprising one or more flexible tubes each comprising a plurality ofapertures at a lower surface thereof to deliver said warm moisture-ladenair to the surface.
 26. An apparatus for de-icing, melting and thawing asurface, the apparatus comprising: a plenum; a flame heated source; oneor more nozzles configured to introduce a spray of aqueous liquid intosaid plenum; a forced air inlet configured for input of forced air intosaid plenum through said flame heated source and said spray of aqueousliquid, thereby producing warm moisture-laden air; and a delivery devicefluidly coupled to an outlet of said plenum and configured to directsaid warm moisture-laden air to the surface.